Conventionally, a core drill is used to drill a hole with a relatively large diameter in materials in which the hole is to be drilled. The core drill includes a cylindrical core body, a shank member which is provided above the cylindrical core body and attached to a chuck disposed at a drive shaft, and cutting chips provided at the peripheral portion of the tip end portion of the core body such that the cutting chips are arranged to be spaced apart from each other. In addition, gullets are formed at portions of the core body, in locations forward relative to the cutting chips in a rotational direction of the core drill, to discharge cutting waste toward a base end of the core drill. At a portion of the core body which is located at a base end side of each gullet, a discharge groove having a spiral shape (tilting shape) is provided to feed the cutting waste toward the base end. In addition to the above constituents, in some core drills, a center drill having a tip end protruding farther than the tip end of the core body is provided at the center of the core body to easily determine a drilling position.
The core drill having the above structure is configured to drill an annular groove which is the same as a rotational trajectory of the cutting chips, deeper, in a material in which a hole is to be drilled, such as wood, resin, metal or a composite material of these, for example, an upper plate of a kitchen unit, thus efficiently drilling a hole with a large diameter substantially equal to the outer diameter of the core drill (see patent literature 1).
After drilling the hole as described above, cylindrical waste is left inside the core body of the core drill.